1. Field of the Invention
The present invention relates to an epoxy resin composition which is useful for encapsulating electric and electronic materials, particularly electric parts such as an adhesive, paint, insulation material and laminate.
2. Description of the Related Art
Recently, for encapsulating semiconductors such as LSI, IC, transistor and the like, transfer molding of an economically useful epoxy resin composition is conducted.
Particularly, surface amounting of LSI is recently conducted, and direct immersion into a solder bath is increasing. Since an encapsulating material is exposed to high temperature in this treatment, moisture absorbed in the encapsulating material expands a, crack is formed in the material, and peeling occurs at an interface with a die pat.
Therefore, the epoxy resin encapsulant is required to have low moisture absorption, high crack resistance and improved adhesion. Further, for obtaining low moisture absorption, an epoxy resin of low viscosity in which a filler can be filled in high concentration is desired. Currently, an encapsulating material in which glycidyl ether of o-cresol novolak is used as a polyfunctional epoxy resin and phenol novolak is used as a curing agent is mainly used, however, when the encapsulating material absorbs moisture in storage, the above-described problems occur. Therefore, for avoiding these problems, the encapsulating material is wrapped for preventing moisture absorption in practical use.
On the other hand, a biphenyl type epoxy resin in current use has a lower viscosity and can contain a filler in higher concentration than a polyfunctional epoxy resin, since the biphenyl epoxy resin is a bifunctional epoxy resin and has a low molecular weight. Therefore, moisture absorption depending on the biphenyl type epoxy resin can be reduced and strength thereof can be increased, consequently, excellent crack resistance can be obtained as compared with an epoxy resin in the form of a glycidyl ether of o-cresol novolak. However, the biphenyl type epoxy resin has the problem that the molding property of a cured article thereof is low as compared with the polyfunctional epoxy resin.
There is also a method in which the molding property is improved by combining the current biphenyl type epoxy resin with the cresol novolak type epoxy resin with maintaining the resin viscosity at suitable level, however, the mixture of the biphenyl type epoxy resin and the cresol novolak type epoxy resin becomes semisolid state (honey-like state) and has no definite shape after melt mixing, therefore, handling property of the resin is insufficient. Further, the mixed resin tends to adhere each other, therefore, there is a problem in handling a large amount of the resin.
On the other hand, a dicyclopentadiene type epoxy resin which has curing ability between that of the biphenyl type epoxy resin and that of the cresol novolak type epoxy resin is commercially available. There is a problem that the dicyclopentadiene type epoxy resin has a low melting point and tends to adhere each other, therefore, the resin should be cooled and preserved, consequently, there is also a problem in handling a large amount of the resin as above.
In addition, the dicyclopentadiene type epoxy resin contains a small number of epoxy groups per unit weight of resin, therefore curing and molding property thereof are sometimes insufficient, and further, heat resistance of the cured and molded article are also sometimes insufficient, since the resin has an alicyclic structure derived from non-reactive dicyclopentadiene.
The biphenyl type bifunctional epoxy resin has a problem that curing and molding property is poor since the number of epoxy functional group is small per one molecule, unlike the cresol novolak type polyfunctional epoxy resin. Specifically, Barcole hardness of the biphenyl type resin slightly lowers in molding as compared with the polyfunctional epoxy resin, therefore, a method for enhancing Barcole hardness has been desired.